Study On Tetra-Needle-Shaped Zinc Oxide Whisker Modifying Nylon 6 And High Density Polyethylene

Toughening semi-crystalline pseudo-ductile polymer by using rigid fillers has become an active area of polymer modification,because a large number of strong and tough materials can be produced by these means.But,due to their own disadvantages,such as the difficulties in phase dispersion and phase structure control,and orientation induced anisotropy,the further application of these modification methods and associated composites is unavailable.So,in this study,the unique 3-dimensional structured filler, tetra-needle-shaped zinc oxide whiskers(T-ZnOw),has been adopted to modify polyamid 6,the typical semi-crystalline pseudo-ductile polymer,in the purpose of obtaining a new kind of composites with high properties.Our attention is mainly focused on how to toughen PA6 with this kind of special fillers and how they function as the modifiers in PA6 matrix,in another words,to find out the mechanism of T-ZnOw toughening the pseudo-ductile polymer,PA6.Under this principle,the impact fracture behavior of T-ZnOw/PA6 composites was carefully studied,as well as its influence factors,which made this thesis consist of three parts:the first part,the effect of interfacial interaction (caused by the coupling agents)on the fracture behavior of T-ZnOw/PA6 composites,investigating the toughening mechanism of T-ZnOw in PA6 matrix; the second part,the study on the fracture behavior of T-ZnOw(s)/PA6 composites, investigating the variation in the impact strength and toughening mechanism caused by the dimension effect of T-ZnOw;the last part,the comparison on the fracture characteristics between T-ZnOw/HDPE and T-ZnOw/PA6 composites, investigating the differences of toughening mechanism brought by the two different polymer matrices.The results showed that:(a)Coupling agents had great influence on the impact fracture behavior of T-ZnOw/PA6 composites.Under satisfying interfacial interaction bought by certain content and type of coupling agent,as well as certain content of T-ZnOw, the toughness of composites could be improved by pull-out,anchoring,bridging and pinning effect of T-ZnOw.(b)The change in T-ZnOw dimension would lead the different C~*(the critical value of T-ZnOw content for toughening)and the different toughening mechanism in PA6 matrix.For T-ZnOw/PA6 composites,the toughening was realized by pull-out,anchoring,bridging and pinning effect during crack propagation.But for T-ZnOw(s)/PA6 composites,the toughness was improved by raising the difficulty of crack initiation,and the crack deflection during crack propagation.(c)The pseudo-ductile polymer,PA6,could be toughened by T-ZnOw effectively,but the ductile polymer,HDPE,could not.The main reason was directly associated with the difference of polymer matrices.For HDPE,the deformation micromechanism was crazing and fibrillation,which could absorb tremendous amount of impact energy and finally gave birth to high toughness;the addition of T-ZnOw,could inspire certain amount of yield deformation and, unfortunately,reduced the resistance of crack propagation,which was attributable to the debonding due to the cavitation at whisker-matrix interface.And,the latter effect triggered the brittle fracture of the composites.(d)T-ZnOw could bring reinforcement effect to the composites,no matter the matrix was the pseudo-ductile polymer,PA6,or the ductile polymer,HDPE.And further study suggested that the reinforcement of T-ZnOw in PA6 matrix was associated to the interfacial interaction and T-ZnOw dimension.Additionally,the T-ZnOw could improved the heat deflection temperature(HDT)largely.